The general objectives of this research are to elucidate the mechanisms and stereochemistry of important reactions in terpene and sterol biosynthesis by chemical synthesis of potential or known enzyme inhibitors, by synthesis of poroiposed intermediates, by stereospecific labeling experiments, and by investigations of biomimetic model reactions. Evaluations of the enzyme inhibitors and biosynthesis with labeled substrates will be performed via collaborations with several biochemical laboratories. The specific aims are summarized below: A. Synthesis of the cyclobutyl disphosphate (PP) isomer of presqualene, aza and carbocyclic PP mimics of intermediates, and the bicyclic ketal triaci core of the squalestatins for evaluation as squalene synthase inhibitors. B. Synthesis of C30 botyrococcene and testing of the preceding squalene synthase inhibitors against botyrococcene synthase. C. Synthesis of aza, phosphonyl, and fluoro analogs of geranylgeranyl diphosphate (GGPP) for evaluation as inhibitors or modified substrates of protein GG transferase (PGGT) and GGPP synthase. D. Determination of the stereochemistry of the CH3->CH2 eliminations in camphene and pinene biosynthesis and the 1,2-hydride shift in sabinene hydrate biosynthesis. E. Investigation of the carbocation rearrangements of silphinyl and caryophyllenyl derivatives as model reactions for cyclopentanoid sesquiterpene biogenesis. F. Study of the catalytic mechanism of skeletal and allylic PP rearrangements as models for terpene cyclase catalysis. High affinity inhibitors of squalene synthase are potentially useful as therapeutic agents for controlling the rate of cholesterol biosynthesis, and avoiding interference with other essential isoprenoid metabolites. Specific PGGT and GGPP synthase inhibitors would have significant biochemical applications as agents that block the prenylation step in the activation of many regulatory and signal-transducing proteins. The fundamental knowledge gained from this research will enhance our understanding of the specificities and catalytic mechanisms of important enzymes associated with the isoprenoid biosynthetic pathway.